Andrew Long
Marine Ecology and Conservation
September 15, 2011
Review: Global Marine Primary Production Constrains Fisheries Catches
The second portion of this article is essentially the discussion of the implications of these findings and more or less the short comings of the researchers’ methods. Essentially this study seeks a correlation or relationship between gross primary production, as measured by satellite quantification of chlorophyll a in surface waters of fishery zones, and fisheries production. It’s a bottom up control analysis of pelagic ecosystems which examines the effects of primary production in terms of net production at the fisheries level.
Conceptually this is a rather kinetic approach to gross production based on the idea of feed conversion ratios and makes a number of assumptions about the structure of trophic webs, fishing pressure, as well as the size, life span, and fecundity of the populations in a given region. Loss of primary production equals less secondary, tertiary, and quaternary production and so on. The researchers normalize spatial productivity in terms of fisheries population based on reported landings, where some areas are more consistently productive than others. Any fisherman will tell you this isn’t a particularly surprising finding. More substantially, a relationship between primary production and landings was indicated by normalizing spatial norms. The verdict is net decrease, which also isn’t surprising. The researchers relegate the decrease in primary production primarily to ocean warming effectively changing spatial productivity. Eventually they conclude that although surface temperatures likely play a key role in influencing the spatial concentration of primary producers, it is the spatial (and quantitative) element of their distribution that is most troubling for fisheries and net production.
Even though researchers showed a strong relationship between these two parameters, the question remains; is this the primary factor contributing to decreased landings? Or has consistent and more precise fishing effort primarily to blame for the decrease? Several studies have found a net decrease in primary production in conjunction with decreased landings in a number of other regional studies. Chassot, et. al. recognized the importance of demonstrating this as a global phenomenon. Taken regionally, one could reason that a net decrease in production is the result of the migratory nature of fish and/or primary producers. Traditionally, this is the mindset. Humbly, at the edge of the sound, men ponder their effects on the seemingly infinite ocean and cannot ascertain their actions could possibly be significant. Arrogantly we ignore the signs.
Another fact this work points to inadvertently, is the effects of primary consumers. The history of Georges Banks groundfish comes to mind. Landings increased consistently off New England until the mid 1900’s, leading up to an enormous collapse of the groundfish population that affected the region for over 20 years, and in many ways still does today. During the end of that period, landings were steadily increasing, but many people fail to realize is that total catch was comprised of many different species. As hake, haddock, and cod landings decreased, gross total landings increased supplanted by of demand for fishmeal from sardines, menhaden, pilchard, and herring, which are used to make agricultural feeds. The collapse and reduction of many of these grazers/primary consumers has major implications and probably accounted for the lasting effects of the groundfish collapse.
Not included in this article, is the interesting and related science of enhancing primary production by utilizing ferrous sulfate. There’s little question that it enhances primary production several fold. However, the initial idea was to sequester carbon dioxide into the phytoplankton and lower global CO2 concentration. It is unknown what proportion of the sequestered carbon dioxide is deposited in the deep ocean via this method as quantification has proven to be elusive. Might this be just the stone we need to kill the two proverbial birds?
Overall, it’s difficult not to come to the realization that global fisheries are essentially facing a “double whammy" of bottom up consequences (as explained here) in the face of top down effects from fishing effort. The paper underscores the increasing pressure fisheries are facing and how fishing at, or over, maximum sustainable yield leaves no margin for error. For example consider how deeply these factors would compound a viral or seasonal suppression of recruitment/survival.
-Chassot, Emmanuel. "Global marine primary production constrains fisheries catches." Ecology Letters 10 (2010): 495-505. ICON. Web. 13 Sept. 2011.
-Molyneaux, Paul. Swimming in Circles: Aquaculture and the End of Wild Oceans. New York: Thunder’s Mouth Press, 2007.
-Woods Hole Oceanographic Institution. Oceanus Vol 46 no.1 (2008): Print.
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